Alumina refractories and methods of treatment

Abstract

Methods for improving the strength of alumina refractory materials are disclosed. The method involves exposing the alumina material to a halogen gas. The treated materials can be used in furnaces for producing fused silica optical members.

What is claimed is:  
     
       1. A method of improving the strength of an alumina refractory material comprising exposing the alumina refractory material to a halogen gas by flowing the halogen gas into a furnace containing the refractory material in the presence of a reducing agent at a temperature between 1000° C. and 1400° C., wherein the exposure to the halogen gas reduces metallic impurities in the material. 
     
     
       2. The method of  claim 1 , wherein the halogen gas is selected from the group consisting of fluorine, iodine, and chlorine. 
     
     
       3. The method of  claim 2 , wherein the gas includes chlorine. 
     
     
       4. The method of  claim 3 , wherein the gas includes a mixture of chlorine and a carrier gas. 
     
     
       5. The method of  claim 4 , wherein the carrier gas includes helium. 
     
     
       6. The method of  claim 1 , wherein the exposing step takes place for at least one hour and less than 10 hours. 
     
     
       7. The method of  claim 1 , wherein the reducing agent is a carbon-containing material. 
     
     
       8. The method of  claim 1 , wherein the four point bend strength of the material is improved by at least 50% by the exposure to the halogen gas. 
     
     
       9. A furnace for the production of fused silica optical members including an alumina refractory material treated in accordance with the method of  claim 1 . 
     
     
       10. A method of improving the strength of an alumina refractory material comprising exposing the refractory material to chlorine gas at a temperature exceeding 1000° C. and for a time exceeding one hour, wherein the exposure improves the four point bend strength of the material by at least 50%. 
     
     
       11. The method of  claim 10 , wherein the step of exposing the refractory material to chlorine gas is performed in the presence of a carbon-containing material. 
     
     
       12. A furnace for the production of fused silica optical members including a refractory treated in accordance with  claim 11 . 
     
     
       13. A method of improving the strength of an alumina refractory material alumina refractory material comprising the step of exposing the alumina refractory material to a halogen gas, wherein the exposing step improves the four point bend strength of the material by at least 50%. 
     
     
       14. The method of  claim 13 , wherein the halogen gas includes chlorine. 
     
     
       15. The method of  claim 13 , wherein the exposing step takes place for at least one hour and less than 10 hours. 
     
     
       16. A furnace for the production of fused silica optical members including an alumina refractory material treated in accordance with the method of  claim 13 .